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  • 1995-1999  (22)
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  • 1
    Electronic Resource
    Electronic Resource
    Integrated micro-scanning tunneling microscope (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2305-2307 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two versions of micro-scanning tunneling microscopes (micro-STMs) have been fabricated. The integrated micro-STMs are fabricated from single crystal silicon using the high-aspect-ratio SCREAM process. Each micro-STM includes integrated xy comb drive actuators and a torsional z actuator with integrated cantilever and tip. One micro-STM measures approximately 200 μm on-a-side and is an example of a STM element for a STM array architecture. Another, larger micro-STM/atomic force microscope measures 2 mm on-a-side including a 1 mm long cantilever with a 20 nm diam tip. We demonstrate the operation of this larger STM by obtaining a STM image of a 200 nm metal conductor on a silicon chip. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115134
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of the temperature dependent phase transition of evaporated Ti films on diamond: Phase identification using maximum entropy data analysis (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3314-3320 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The carbidization of thin Ti films on natural diamond has been investigated in the temperature range between room temperature and 700 °C using x-ray-photoelectron-spectroscopy. It is possible to separate chemical phases in Ti 2p3/2 electron peaks after deconvolution of the spectrometer's broadening function. We employ Bayesian information, using maximum entropy prior information. The apparatus function is derived from measured spectra of the Fermi edge of a silver sample. Data analysis of reconstructed Ti 2p3/2 core level spectra shows that, with increasing temperature, Ti films are transformed from metallic Ti to a mixed phase consisting of metallic Ti and TiC0.56. No carbidic phase is found with a ratio of carbidic C to Ti smaller than 0.56. The metallic layer is fully transformed to TiC0.56 at 430 °C. At higher temperatures, the concentration ratio of carbidic C to Ti depends nearly linearly on temperature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365640
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  • 3
    Electronic Resource
    Electronic Resource
    Surface micromachined interferometer-based optical reading technique (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3324-3326 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A surface micromachined suspended interferometer and an atomic force microscope (AFM) are incorporated into a novel optical reading technique. The AFM tip mechanically deflects the suspended membrane as it scans past a data bit on the membrane surface. The data are read by monitoring the changing interference pattern generated in the optical aperture of the interferometer. When operated in parallel, there exists the potential for high speed, high density data reading. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117294
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  • 4
    Electronic Resource
    Electronic Resource
    Optical reading and writing on GaAs using an atomic force microscope (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2780-2782 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optically aided reading and writing of gold and tungsten mounds on proton-implanted, multiple quantum well InGaAs/GaAs wafers has been demonstrated using an atomic force microscope (AFM). The system is relatively simple, requiring only a diode laser as the light source, providing a novel, compact, optoelectronic memory system. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113473
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  • 5
    Electronic Resource
    Electronic Resource
    Altered Calcium Homeostasis in Cells Transformed by Mitochondria from Individuals with Parkinson's Disease (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 68 (1997), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Parkinson's disease may be linked to defects in mitochondrial function. Mitochondrially transformed cells (cybrids) were created from Parkinson's disease patients or disease-free controls. Parkinson's disease cybrids had 26% less complex I activity, but maintained comparable basal calcium and energy levels. Parkinson's disease cybrids recovered from a carbachol-induced increase in cytosolic calcium 53% more slowly than controls even with lanthanum and thapsigargin blockade. Inhibition of complex I with the Parkinson's disease-inducing metabolite 1-methyl-4-phenylpyridinium (MPP+) similarly reduced the rate of recovery after carbachol. This MPP+-induced reduction in recovery rates was much more pronounced in control cybrids than in Parkinson's disease cybrids. Parkinson's disease cybrids had less carbonyl cyanide m-chlorophenylhydrazone-releasable calcium. Bypassing complex I with succinate partially restored Parkinson's disease cybrid, and MPP+ suppressed control cybrid recovery rates. The subtle alteration in calcium homeostasis of Parkinson's disease cybrids may reflect an increased susceptibility to cell death under circumstances not ordinarily toxic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1997.68031221.x
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlinear Least-Squares Minimization Applied to Tracer Gas Decay for Determining Airflow Rates in a Two-Zone Building (1997)
    Oxford, UK : Munksgaard International Publishers
    Indoor air 7 (1997), S. 0 
    Details
    ISSN: 1600-0668
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Medicine
    Notes: Abstract We developed a method based on tracer gas decay measurements to quantify the airflow rates, including the interzonal airflows, in a two-zone building: different tracer gases were simultaneously pulse-injected into each of the two zones and the evolution of the gas concentrations in each zone was measured; theoretical concentration profiles obtained by solving dynamic material-balance equations for two coupled, well-mixed zones were fit to the experimental data using nonlinear least-squares minimization; and estimates of the airflow rates were iteratively refined until a best fit was achieved between the model and the data. We conducted experiments validating the method in two full-sized rooms of a test house. Airflows were controlled using blowers, and mixing was ensured by the use of fans. Airflow rates inferred by the tracer gas technique agreed with imposed airflow rates within an average absolute error of 8%. Results are also reported for two experiments conducted in the same structure under uncontrolled conditions. Goodness-of-fit tests revealed no statistically significant differences between measured tracer gas concentrations and theoretical concentration profiles constructed using the least-squares parameter estimates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0668.1997.t01-1-00008.x
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  • 7
    Electronic Resource
    Electronic Resource
    A Genetic Algorithm for the Ab Initio Phasing of Icosahedral Viruses (1996)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 235-251 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Genetic algorithms have been investigated as computational tools for the de novo phasing of low-resolution X-ray diffraction data from crystals of icosahedral viruses. Without advance knowledge of the shape of the virus and only approximate knowledge of its size, the virus can be modeled as the symmetry expansion of a short list of nearly tetrahedrally arranged lattice points which coarsely, but uniformly, sample the icosahedrally unique volume. The number of lattice points depends on an estimate of the non-redundant information content at the working resolution limit. This parameterization permits a simple matrix formulation of the model evaluation calculation, resulting in a highly efficient survey of the space of possible models. Initially, one bit per parameter is sufficient, since the assignment of ones and zeros to the lattice points yields a physically reasonable low-resolution image of the virus. The best candidate solutions identified by the survey are refined to relax the constraints imposed by the coarseness of the modeling, and then trials whose intensity-based statistics are comparatively good in all resolution ranges are chosen. This yields an acceptable starting point for symmetry-based direct phase extension about half the time. Improving efficiency by incorporating the selection criterion directly into the genetic algorithm's fitness function is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444995011620
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  • 8
    Electronic Resource
    Electronic Resource
    Metastable Equilibrium Solubility Behavior of Bone Mineral (1999)
    Springer
    Calcified tissue international 64 (1999), S. 329-339 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Carbonated apatites — Bone mineral — Solubility — Crystallinity — Calcium phosphates.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Previous studies have shown that carbonated apatites with a range of carbonate contents and crystallinities exhibit the phenomenon of metastable equilibrium solubility (MES) distributions. The purpose of the present study was to investigate the solubility behavior of bone mineral using the concepts of MES and MES distributions and, together with crystallinity and chemical composition data, examine the similarity of bone mineral to carbonated apatite (CAP). Bone samples were harvested from 1-, 5-, and 8-month-old rats. The organic components of the bone samples were removed by hydrazine deproteination. Carbonated apatite was synthesized by the hydrolysis of dicalcium phosphate dihydrate (DCPD) in a NaHCO3-containing media at 50°C. The MES distributions of bone mineral and CAP were determined by equilibrating predetermined amounts of CAP or bone mineral in a series of 0.1 M acetate buffers containing calculated levels of calcium and phosphate and maintained at essentially constant pHs of 5.0, 5.3, 5.7, and 6.5. From the compositions of the equilibrating buffer solutions, ion activity products based upon the stoichiometries of octacalcium phosphate, hydroxyapatite, and carbonated apatite were calculated in an attempt to determine the function governing the dissolution of CAP and bone mineral. The results of this study demonstrated that the MES distribution phenomenon appeared to hold for bone mineral and that the changes in crystallinity of bone mineral with age correlated well with changes in the MES values. A CAP sample was prepared that was found to be an excellent synthetic prototype closely mimicking the physicochemical behavior of bone mineral from an 8-month-old rat. Another finding of this study was that the ion activity product function based upon the hydroxyapatite stoichiometry well described the MES results obtained with both CAP and bone mineral. The interpretation that a surface complex with hydroxyapatite stoichiometry governs the solubility behavior of bone mineral is, therefore, consistent with the experimental data. Other calcium phosphate stoichiometries for the surface complex showed systematic variations in the MES profiles when the pH of the equilibrating solution was varied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900628
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  • 9
    Electronic Resource
    Electronic Resource
    Ovariectomy-Induced Changes in Aged Beagles: Histomorphometry of Rib Cortical Bone (1998)
    Springer
    Calcified tissue international 62 (1998), S. 237-243 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Cortical bone — Dog — Histomorphometry — Sequential rib biopsies — Postmenopausal osteoporosis.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Bone loss associated with estrogen depletion is well documented in cancellous bone but less well characterized in cortical bone. The effects of ovariectomy on the aged beagle skeleton were studied by histomorphometric analysis of the cortical bone in sequential rib biopsies. Biopsies were taken from each ovariectomized or sham-operated dog at the time of surgery and at 1, 4, and 8.5 months after surgery. Just prior to each postoperative biopsy, tetracycline, calcein, and xylenol orange, respectively, were administered by a fluorochrome labeling procedure (2d-10d-2d) to provide markers of bone formation. Analysis of sequential rib biopsies provided a means to follow the ovariectomy response over time and to compare each animal against its own baseline. Though ovariectomy did not influence histomorphometric indices at 1 month after surgery, a transient increase in cortical bone formation occurred thereafter, with a sixfold increase over that of sham-operated dogs at 4 months (P 〈 0.001) and a return to near control levels at 8.5 months. Cortical porosity increased by the fourth month after ovariectomy and remained high at 8.5 months. These data demonstrate for the first time that rib cortical bone is a responsive site for the effects of ovariectomy in aged female dogs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900423
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of Estrogen Deficiency on Cancellous and Cortical Bone Structure and Strength of the Femoral Neck in Rats (1997)
    Springer
    Calcified tissue international 61 (1997), S. 336-344 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Ovariectomy — Femoral neck — DEXA — Histomorphometry — SEM — Mechanical testing.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Eighty mature Sprague-Dawley rats were weight matched before ovariectomy (Ovx) or Sham surgery (Sham). Sham rats had free access to food and water throughout the experiment, whereas Ovx rats were kept on the pair-fed diet. Rats were euthanized at 4, 8, and 12 weeks after surgery, and had received fluorochrome bone markers at 9 and 2 days prior to euthanasia. In addition 10 rats were euthanized at the time of surgery serving as baseline controls. All rats were also scanned for body composition and bone mineral parameters by DEXA before surgery and euthanasia. Left proximal femurs (femoral necks) were used for bone histomorphometry, whereas right femurs were used for in vitro DEXA measurements and mechanical testing. Despite pair-feeding, ovariectomized rats had increased body weights and fat body mass, whereas the percent lean body mass steadily declined throughout the experiment. Mineral density of the whole femur and femoral neck was significantly higher in the Sham rats relative to Ovx animals. Ovariectomy reduced trabecular number and thickness, and increased trabecular separation and bone marrow space at the femoral midneck location. The structure of the remaining trabeculae was dramatically changed toward simpler struts as revealed by nodal analyses. Cortical thickness in Ovx rats was reduced because of the high endocortical resorption, which, in addition to cancellous bone resorption, resulted in fewer endocortico-trabecular connections. Femoral necks obtained from ovariectomized rats had reduced strength and were less stiff relative to controls. Because of the enormous clinical significance of the proximal femur for osteoporosis in humans, and the opportunity for studying bone BMD, mass, structure, and strength at the same skeletal location, the femoral neck appears superior to other skeletal sites routinely used for bone histomorphometry or mechanical testing in the Ovx rat model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002239900344
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